Semiconductor packaging typically involves forming a bump on a substrate, e.g., a solder bump on a wafer. Such bumps can be formed by various techniques such as electroplating, vapor deposition, printing, and ball-bumping. The continuous increase in I/O terminals on semiconductor chips and small pitches of interconnections have led to wider use of electroplating, which can provide fine structure metallization and higher yields. Electroplating processes can be generally categorized in two types. In a fountain or cup type process, a substrate, such as a semiconductor wafer, is plated while the surface to be plated faces downward into a plating solution supplied upwardly to metalize the surface. In a dip type process, the substrate is vertically placed in a plating vessel and the solution is supplied from the bottom to overflow the top of the plating vessel.
Plating tools must be capable maintaining high throughput and bump uniformity. Performance of a plating tool is very dependent on the consistency and control of the solution flow to the wafer. The composition of a solder bump depends on the plating bath composition, plating rate, and plating area. Various semiconductor wafers are designed for different industrial applications, such as microprocessors, smart phones, mobile phones, cellular handsets, set-top boxes, DVD recorders and players, automotive navigation, printers and peripherals, networking and telecom equipment, gaming systems, and digital cameras. Consequently, various wafers are designed to be plated with different solder bump patterns. Solder bump patterns may differ in the array or arrangement, number, pitch and/or size, e.g., diameter, of the solder bumps. It is difficult, however, to maintain solder bumps at a uniform concentration, particularly at a uniform concentration from wafer-to-wafer, as where the wafers are electroplated with different solder bump patterns, in the same plating tool without sacrificing throughput. If the plating rate is adjusted to maintain a uniform solder bump composition, throughput is sacrificed, because a constant plating rate must be maintained to achieve a high throughput. It is also very difficult to electroplate different wafers with solder bumps having different predetermined or targeted compositions in the same plater without reducing throughput. The highly competitive marketplace requires high throughput for survival.
A need therefore exists for methodology enabling the electrodeposition of a pattern of solder bumps having a uniform composition. A particular need exists for methodology enabling the electrodeposition of different patterns of solder bumps on different wafers at a uniform solder bump composition, or at different predetermined compositions, at the same high throughput.